This application is to continue and extend an ongoing 4-center, NHLBI-funded study (Sleep AHEAD, Action for Health in Diabetes) whose primary goal is to assess the effects of weight loss on sleep-disordered breathing (SDB) among obese patients with both type 2 diabetes (T2DM) and obstructive sleep apnea (OSA). Sleep AHEAD has been very successful logistically and scientifically. We enrolled 296 participants with sleep apnea, greatly exceeding our goal (191% of target), and established an efficient infrastructure to perform unattended home polysomnograms (PSG) at baseline and 1-, 2-, and 4-year follow-ups. We have assembled and retained the world's largest cohort of obese patients with OSA and T2DM. Moreover, the participants are well characterized by virtue of simultaneous enrollment in Look AHEAD, a 16-center; NIDDK-funded study to examine the long term effects of a weight loss intervention on cardiovascular events, including cardiovascular disease-related mortality. This NIDDK study also provides state-of-the-art weight management strategies in the context of a randomized controlled trial. Thus, the Sleep AHEAD participants, a cohort that we have found to be at extraordinarily high risk for OSA based on obesity and T2DM, are ideal for assessing the long-term effects of weight changes on SDB. In addition, as we propose in this competitive renewal, we can compare 4-5 year longitudinal changes in both SDB and sleep architecture between our Sleep AHEAD cohort, all of whom have T2DM, to carefully matched patients without T2DM from the Sleep Heart Health Study (SHHS). Such comparisons are made feasible since the data from both cohorts are already collected and the PSG methodologies are virtually identical. This application extends the 1-, 2- and 4-year findings of Sleep AHEAD by examining changes in weight and SDB among 296 obese patients with OSA and T2DM over a 10-year period. In addition, we propose to determine the effects of T2DM on SDB and sleep architecture by utilizing well-matched controls without T2DM from the SHHS. The proposed research has three specific aims: 1) to assess the effects of weight loss at 1-year on sleep-disordered breathing at 10 years; 2) to assess changes in sleep-disordered breathing between those with and without type 2 diabetes; and 3) to assess changes in sleep architecture between those with and without type 2 diabetes.